If you want better sound, in a retail box, get a moderately priced professional USB interface. You'll never use the mic features, but the quality for the price will be better than a consumer sound card nonetheless. With headphones, I've yet to hear a quiet, unveiled, onboard audio implementation, with an active dGPU (IE, gaming with headphones). 5.1 and 7.1 are pre-mixed, so placement really counts, though you can probably adjust levels.
If you want software licenses (Dolby Headphone, Dolby DTS encoding, and other similar things), get a consumer PC sound card. That's their real value. What is it that is specifically lacking with your onboard?